is it possible to apply for a visa in Thailand or should I apply in my country? and if it is OK to apply here.

If you plan to apply in Thailand, you are required to provide your valid stay permit, resident permit for employment or study, for example. Other documents are your passport, filled application form, a recent passport photo, an invitation letter/round-trip air tickets and hotel booking.

thank you for the fast replay

any how I am staying in Thailand using a Non-B visa is that acceptable ?

Yes, you can apply with it if you mean Non-Immigrant Visa “B” for (business and work) there.

that is it ... thanks :) can i ask about the invitation litter ? what is it exactly ?

An invitation letter from your friend with following details:
(1) Information on the applicant (full name, gender, date of birth, etc.)
(2) Information on the planned visit (arrival and departure dates, place(s) to be visited, etc.)
(3) Information on the inviting individual (name, contact telephone number, address, signature of the inviting individual)